Buggy code:
public class ProxyControl extends GenericController implements Serializable { private static final Logger log = LoggingManager . getLoggerForClass ( ) ; private static final String HTTP_TEST_SAMPLE_GUI = HttpTestSampleGui . class . getName ( ) ; private static final String ASSERTION_GUI = AssertionGui . class . getName ( ) ; private static final String LOGIC_CONTROLLER_GUI = LogicControllerGui . class . getName ( ) ; private static final String HEADER_PANEL = HeaderPanel . class . getName ( ) ; private transient Daemon server ; public static final int DEFAULT_PORT = 8080 ; public static final String DEFAULT_PORT_S = Integer . toString ( ProxyControl . DEFAULT_PORT ) ; private static PatternCacheLRU patternCache = new PatternCacheLRU ( 1000 , new Perl5Compiler ( ) ) ; transient Perl5Matcher matcher ; public static final String PORT = "ProxyControlGui.port" ; public static final String EXCLUDE_LIST = "ProxyControlGui.exclude_list" ; public static final String INCLUDE_LIST = "ProxyControlGui.include_list" ; public static final String CAPTURE_HTTP_HEADERS = "ProxyControlGui.capture_http_headers" ; public static final String ADD_ASSERTIONS = "ProxyControlGui.add_assertion" ; public static final String GROUPING_MODE = "ProxyControlGui.grouping_mode" ; public static final String USE_KEEPALIVE = "ProxyControlGui.use_keepalive" ; public static final String REGEX_MATCH = "ProxyControlGui.regex_match" ; public static final String HTTPS_SPOOF = "ProxyControlGui.https_spoof" ; public static final int GROUPING_NO_GROUPS = 0 ; public static final int GROUPING_ADD_SEPARATORS = 1 ; public static final int GROUPING_IN_CONTROLLERS = 2 ; public static final int GROUPING_STORE_FIRST_ONLY = 3 ; private long lastTime = 0 ; private static final long sampleGap = JMeterUtils . getPropDefault ( "proxy.pause" , 1000 ) ; private boolean addAssertions ; private int groupingMode ; private boolean useKeepAlive ; private boolean regexMatch = false ; private JMeterTreeNode target ; public ProxyControl ( ) { } public void setPort ( int port ) { } public void setPort ( String port ) { } public void setCaptureHttpHeaders ( boolean capture ) { } public void setGroupingMode ( int grouping ) { } public void setAssertions ( boolean b ) { } public void setUseKeepAlive ( boolean b ) { } public void setIncludeList ( Collection list ) { } public void setExcludeList ( Collection list ) { } public void setRegexMatch ( boolean b ) { } public void setHttpsSpoof ( boolean b ) { } public String getClassLabel ( ) { } public boolean getAssertions ( ) { } public int getGroupingMode ( ) { } public int getPort ( ) { } public String getPortString ( ) { } public int getDefaultPort ( ) { } public boolean getCaptureHttpHeaders ( ) { } public boolean getUseKeepalive ( ) { } public boolean getRegexMatch ( ) { } public boolean getHttpsSpoof ( ) { } public Class getGuiClass ( ) { } public void addConfigElement ( ConfigElement config ) { } public void startProxy ( ) { } public void addExcludedPattern ( String pattern ) { } public CollectionProperty getExcludePatterns ( ) { } public void addIncludedPattern ( String pattern ) { } public CollectionProperty getIncludePatterns ( ) { } public void clearExcludedPatterns ( ) { } public void clearIncludedPatterns ( ) { } public JMeterTreeNode getTarget ( ) { } public void setTarget ( JMeterTreeNode target ) { } public void deliverSampler ( HTTPSamplerBase sampler , TestElement [ ] subConfigs , SampleResult result ) { } public void stopProxy ( ) { } boolean filterUrl ( HTTPSamplerBase sampler ) { } private void addAssertion ( JMeterTreeModel model , JMeterTreeNode node ) throws IllegalUserActionException { ResponseAssertion ra = new ResponseAssertion ( ) ; ra . setProperty ( GUI_CLASS , ProxyControl . ASSERTION_GUI ) ; ra . setName ( "Check<seq2seq4repair_space>response" ) ; <START_BUG> ra . setTestField ( RESPONSE_DATA ) ; <END_BUG> model . addComponent ( ra , node ) ; } private void addDivider ( JMeterTreeModel model , JMeterTreeNode node ) throws IllegalUserActionException { } private void addSimpleController ( JMeterTreeModel model , JMeterTreeNode node , String name ) throws IllegalUserActionException { } private void addTimers ( JMeterTreeModel model , JMeterTreeNode node , long deltaT ) { } private JMeterTreeNode findFirstNodeOfType ( Class type ) { } private JMeterTreeNode findTargetControllerNode ( ) { } private Collection findApplicableElements ( JMeterTreeNode myTarget , Class myClass , boolean ascending ) { } private void placeSampler ( HTTPSamplerBase sampler , TestElement [ ] subConfigs , JMeterTreeNode myTarget ) { } private void removeValuesFromSampler ( HTTPSamplerBase sampler , Collection configurations ) { } private String generateMatchUrl ( HTTPSamplerBase sampler ) { } private boolean matchesPatterns ( String url , CollectionProperty patterns ) { } private void replaceValues ( TestElement sampler , TestElement [ ] configs , Collection variables ) { } private void notifySampleListeners ( SampleEvent event ) { } private void notifyTestListenersOfStart ( ) { } private void notifyTestListenersOfEnd ( ) { } public boolean canRemove ( ) { } }

Fix:
ra . setTestFieldResponseData ( ) ;